Four independent antigenic determinants on the capsid polypeptides of aphthovirus

Four independent antigenic determinants in the virus capsid have been defined in radioimmunoassay tests using antisera prepared against isolated structural polypeptides VP1, 2 and 3. Only one determinant was detected on the intact particle and it was contained within VP1 (called the VP1-A determinant). Three determinants were found on the 12S subparticle, two contained within VP1 (VP1-A and VP1-B determinants) and one contained within VP2 (VP2 determinant). The fourth determinant was contained within VP3 (VP3 determinant) and could only be detected when the virus was disrupted to individual polypeptides. It is concluded that the VP1-A determinant is likely to be of epidemiological importance since (i) it was present on the intact virion, (ii) variation at this determinant was detected with heterologous field strains, (iii) it contained a determinant responsible for the induction of neutralizing antibodies and (iv) it was an antigenic component of the trypsin-sensitive region of VP1 which has been shown previously by several workers to be of critical importance in the immunogenicity of the virus.